1. Field of the Invention
This invention relates to check valves. More particularly, this invention relates to check valves having a pre-set cracking pressure.
2. Description of the Background Art
Presently, there exist many types of check valves designed to control the one-way flow of a fluid therethrough. More particularly, one predominant type of check valve comprises a ball reciprocatingly positioned within a caged area of a fluid passageway. The flow of fluid in one direction through the passageway is uninhibited (unchecked) as it flows around the ball to exit the passageway. However, in the opposite direction, the flow of fluid forces the ball against a valve seat, thereby inhibiting (checking) the flow of fluid therethrough. Many variations of this basic embodiment of a check valve have been developed over the past many decades that check valves have been in use, each having certain advantages when used in certain applications.
In one application area, check valves, commonly referred to as "catheter" check valves, have been developed to control the one-way flow of a fluid into an inflatable bulb of a catheter or endotracheal tube or in similar relatively low-pressure applications. Indeed, due to the relatively low back pressure exerted on the valve element to urge it against the valve seat, it is usually desirable to provide means for constantly urging the valve element against the valve seat such that the valve remains closed when little or no back pressure is present. Consequently, check valves of this nature have a pre-set cracking pressure which must be exerted on the valve element to unseat itself from the valve seat allowing the flow of the fluid in the unchecked direction.
For example, U.S. Pat. No. 3,831,629, the disclosure of which is hereby incorporated by reference herein, discloses a check valve comprising a valve element which is constantly urged in sealing engagement with a valve seat thereby maintaining the valve in a closed condition even during the complete absence of back pressure exerted on the valve. Moreover, a certain amount of forward cracking pressure must be exerted on the valve element in the unchecked direction to unseat the valve element, allowing the flow of fluid therethrough. As illustrated and discussed in said patent, such positive cracking pressure may be overcome by means of a mechanical instrument, such as a syringe, by fluid pressure, or by a combination of the same.
After more than a decade of experience with the check valve disclosed in said patent, the Assignee of said patent and of this application, has realized that there are some disadvantages associated with the check valve manufactured in accordance with that patent. First, while the valve element may be mass-produced for use in a large variety of valves, differently dimensioned valve bodies or valve elements must be produced in order to provide a variety of valves having different cracking pressures. Consequently, a significant inventory of injection molds and related equipment must be continually developed depending upon the needs of each particular customer. Thus, the ability to provide check valves of this nature with different degrees of cracking pressures necessarily results in an increase in the cost of manufacture because of the inability to produce a universal body usable in conjunction a universal valve element to produce different valves having different cracking pressures.
Therefore, it is an object of this invention to provide an apparatus which overcomes the aforementioned inadequacies of the prior art devices and provides an improvement which is a significant contribution to the advancement of the check valve art.
Another object of this invention is to provide a check valve having a pre-set cracking pressure which maintains the check valve in a closed position even when no back pressure is exerted by the fluid on the valve element to seat the same against the seat of the check valve.
Another object of this invention is to provide a check valve having a pre-set cracking pressure comprising a universal valve element positioned within a universal body such that check valves having different cracking pressures can be produced by utilizing universal injection molds for the body and for the valve element thereby decreasing the cost of manufacture.
Another object of this invention is to provide a check valve having a valve element constantly urged against a valve seat by means of an insertable, apertured plug positioned in the output passageway of the check valve in engagement with the valve element.
Another object of this invention is to provide a check valve comprising a valve element urged against a valve seat by means of an insertable, apertured plug, wherein differently sized plugs may be provided to increase or decrease the cracking pressure of the valve.
The foregoing has outlined some of the more pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.